Arterial blood, which supplies the heart muscle, is able to pass through healthy heart tissue while nourishing the same, yet has difficulty reaching ischemic tissue. As a result, the supply of ischemic tissue with nutrients and the discharge of metabolic catabolites from such ischemic tissue will be impaired.
In this context, it has already been proposed to supply ischemic tissue with blood through retrograde perfusion. This means that blood is attempted to be allowed to flow back from the coronary sinus through the coronary venous system in counterflow by feeding blood from a different source into the coronary sinus, either by permanently connecting an artery with the coronary sinus or by temporarily inserting a catheter into the sinus, which catheter is supplied with blood taken from a remote artery and transported by the aid of a blood pump located outside the patient's body.
Another technique proposed for retroperfusion uses an inflatable balloon which is fixed to the end of a catheter to intermittently occlude the coronary sinus. The blood pressure in the coronary sinus rises during the occlusion at every heart beat so as to cause blood reaching the coronary sinus through the healthy tissue of the heart muscle to be flushed back into the ischemic tissue. For such an intermittent coronary sinus occlusion, the balloon end of the catheter is inserted either percutaneously or surgically. The other end of the catheter is supplied with a gas or fluid by a pump which causes the cyclic inflation and deflation of the balloon.
A typical application of blood retroinfusion in coronary veins through intermittent coronary sinus occlusion applies to myocardial protection during a short-term coronary arterial occlusion in the context of a cardiologic intervention. A typical such intervention comprises, for instance, the balloon dilatation of an arteriosclerotically constricted coronary artery. That method, which is also known as percutaneous transluminal coronary angioplasty (PTCA), comprises the conduction of a balloon catheter into the region of the coronary artery stenosis under X-ray control and the compression of the osclerotic plaque by the inflation of the balloon, which is located on the end of the catheter. During the dilatation of the balloon, no supply of the tissue with oxygen-containing blood takes place downstream in the artery with functional changes in the ischemic area of the myocard being detectable already at dilatations lasting longer than 30 seconds. Consequential problems of the ischemic protection of the myocard will also be faced with other interventions aimed at coronary vascularization such as, e.g., atherectomy, coronary endoprostheses and laser applications.
A device for the retroinfusion of coronary veins is, for instance, known from U.S. Pat. No. 4,934,996, by which a pressure-controlled, intermittent coronary sinus occlusion can be performed. The device comprises a means for occluding the sinus such as, e.g., an inflatable balloon catheter, a pressure measuring unit for measuring the fluid pressure within the coronary sinus and a control unit which generates triggering signals for the occlusion device to trigger or release an occlusion. The control unit is devised in a manner that the pressure maximum in the coronary sinus is measured during every heart beat, a plateau value of the pressure maxima of consecutive heart beats is estimated by calculation and the occlusion of the coronary sinus is released on the basis of the plateau value of the pressure maxima.
The occlusion of the coronary sinus causes a pressure increase and, as a result, a retroperfusion of blood via the respective vein into the nutritive capillaries of the ischemic area so as to enable the supply of nutrients to that area. At a release of the occlusion, the retroperfused blood is flushed out while the metabolic waste products are carried off at the same time. In the method according to U.S. Pat. No. 4,934,996, a systolic pressure curve is, thus, estimated based on the measurement of the pressure maximum in the coronary sinus during every heart beat, with the intermittent occlusion being controlled as a function of the plateau value of the systolic pressure curve. The course of the estimated systolic pressure curve also allows for a conclusion as to the efficiency of the heart, with the slope of the curve reflecting, for instance, the contractibility of the heart.
Under certain circumstances, the determination of the moment of release of the occlusion by way of plateau values of the systolic pressure curve according to U.S. Pat. No. 4,934,996 is, however, not feasible with sufficient accuracy.